More important but vague high-ranking officer (5,7)
I believe the answer is:
major general
'high-ranking officer' is the definition.
'major general' can be an answer for 'officer' (I've seen this before). I'm unsure of the 'high-ranking' bit.
'more important but vague' is the wordplay.
'more important' becomes 'major' (I've seen this before).
'but vague' becomes 'general' (I've seen this in another clue. I am not sure about the 'but' bit.).
'major'+'general'='MAJOR-GENERAL'
Can you help me to learn more?
(Other definitions for major general that I've seen before include "Stanley the model of a modern one (G & S)" , "army officer" , "Two officers meeting" .)